Agent for adding to a mould in which molten ferritic stainless steel is cast by a continuous casting process

ABSTRACT

An agent for adding to a mould in which molten ferritic stainless steel is cast by continuous casting process characterized by containing 20 to 35 percent by weight of fly ash, 30 to 40 percent by weight of Portland cement and/or blast furnace slag, 20 to 27 percent by weight of fluorspar, 2 to 15 percent by weight of one or more of a carbonate, silicate and the like, 5 to 10 percent by weight of one or more of a fluoride, silicofluoride and the like and 5 to 10 percent by weight of one or more of such carbonaceous substances as coke, graphite and charcoal, and having a melting point of 1,000* to 1,100* C and a viscosity of 0.1 to 5.0 poise at 1,500*C and an average particle size less than 100 meshes.

(3 United stateS Patent 1 1 Kishida et al. 51 Jan. 2, 1973 [541 AGENT FOR ADDING TO A MOULD IN WHICH MOLTEN FERRITIC [56] References Clted STAINLESS STEEL IS CAST BY A CONTINUOUS CASTING PROCESS UN'TED STATES PATENTS 3,262,165 7/1966 lngham ..106/38.22 X [75] Inventors. Tohru Klshlda, Wakayama-shr,

wakayamzbken; Tadashi Arikawa 3,607,234 9/1971 Kawawa et al. ..106/97 5:32; b lfigfiy gf x mg' Primary Examiner-Lorenzo B. Hayes ken; SIIinobu Fukushlge, lmaichi- Attamey-xenwood Ross et ShI, Tochigi-ken, all Of Japan [73] Assignees: Sumitomo Metal Industries, Ltd., An 3 gent for adding to a mould n yh el mgltgn fer- Osaka'sh" osaka'fu Mkoh ritjg stainless steel is cast by continuous casting Tokyo Japan process characterized by containing 20 to 35 percent [221 Filed: Aug. 5, 1911 gy g s LLQ L A L2L9 1YJ E8hI 0 ans: ggmeqt an o urnace s a 39 [21] App]v No.. 169,366 pgrcem by \yqigl t g f uOrS ar, 2,819.1 PQ HLPX weight of one or moreo a car onatg and the [30] Foreign Application Priority Data g l0 1: y Welg rz 2 1 8 of a uorr e, s1 ico uongeandihe 1 e an to e Aug. 12, 1970 Japan ..4s/70043 W one or more (Each garbonmgns m a fifisge xegmphi eaniin. W having [52] U.S. Cl. ..l06/38.27, 106/3828, 106/383, a melting point of 10008 to oooc and a viscosity of I t Cl gg2 0.1 to 5.0 poise at 1,500C and an average particle 11 1 h 100 h [58] Field of Search....106/38.27, 38.22, 38.28, 38.3, me mes es 1 Claim, 1 Drawing Figure PATENTEDJAN 2 ma INVENTORS TOHRU KISHIDA TADASHI ARIKAWA SHIGERU MATSUYAMA sumoau FUKUSHIGE BY Kmmd 5 chumf la/um ATTORNEYS AGENT FOR ADDING TO A MOULD IN WHICH MOLTEN FERRITIC STAINLESS STEEL IS CAST BY A CONTINUOUS CASTING PROCESS The present invention relates to an agent for adding 5 to a mould in which molten ferritic stainless steel is cast by a continuous casting process.

Various methods of improving the surfaces of products in a continuous casting of steels have been made since its early days. That is to say, there have been taken methods of preventing sticking by early cooling and solidifying a poured molten metal by using a copper alloy having a high thermal conductivity and giving a motion to the mould, of preventing nonmetallic inclusion from mixing into the molten metal by improving the refractory materials of the tundish and ladle and of preventing the oxidization of the molten metal by imersing the nozzle. Further, in the operation, there has been taken a means of uniforming the production of a solidified layer of a poured molten 0 metal by setting a proper value of the molten metal pouring velocity and the mould has been lubricated and the oxidization of the molten metal surface near the top part of the mould has been prevented by adding a lubricating oil to the mould wall. Further, an invention to prevent oxidization and absorb nonmetallic inclusion in the molten metal by producing a powder layer and a high viscosity melt layer by adding a coating powder for the prevention of the oxidization of the molten metal surface has been proposed. Though various improvements have been made in the machines and apparatus, it is a fact that particularly the perfect prevention of the oxidization and cooling of the surface of the poured molten metal in the mould and the 5 proper lubrication of the mould wall are still absolutely necessary in the operation to obtain ingots of a high quality. However, in the above mentioned method wherein a lubricating oil is fed to the mould wall, the oil is decomposed by the heat of the melt and loses the lubricating property and it is difficult to attain the object. Further, in the method wherein a coating powder is added to the molten metal bath surface to form a high viscosity melt layer in the lower layer and form an unmolten powder layer above it, there is an effect of 5 preventing oxidation but there is no effect of lubricating the mould wall and there is a defect that, in case a high viscosity melt is deposited on the mould wall, it is caused to be wound into the surface and produces surface flaws. Thereafter, there has been obtained an effect of decresing the ingot surface flaws and hypodermic pinholes by using a composition comprisins 3.9% a 9%??(5 14 h a. 2 2 s qf, ,C as aneirarnple by the improvement of the additive powder so that the molten metal bath surface may be 5 kept warm, at the same time a melt layer may be formed on the molten metal contact surface, nonmetallic inclusion in the molten metal may be absorbed and said melt may become a lubricant for the mould and may be led out of the mould together with the cast ingot while protecting the cast ingot surface. However, such composition as is mentioned above is recognized to decrease the cast ingot surface flaws and simplify the subsequent treatment if it is only made to have a fusible component in the case of any other kinds of steels than ferritic stainless steels but, in ferritic stainless steels, even if an operation of removing the surface flaws of the cast ingot is made subsequently, heat cracks are generated and, when the ingot is rolled, they become expanded flaws, no product can be made, therefore the ingot is cut off, the yield of the product is influenced and the process is complicated. The flaw removing operation producing no heat crack is very difficult. In fact. a casting operation producing no surface flaw at all is required and the situation is different from that of the case that, as in an ordinary steel or low alloy steel, if flaws are removed, there is no trouble in rolling.

Even the slightest flaw on the surface of the continuous cast ingot of a ferritic stainless steel causes a defective rolling as mentioned above. In case the fusibility of the powder added to the molten steel surface is low, that is to say, when the molten fluidity is low as a whole, the powder is granulated between the mould wall and the solidified film of the molten steel and is wound into the solidified shell of the molten steel during the production, flaws are generated in those places and, even if the greater part of the powder forms a melt high in the fluidity and performs a lubricating action between the mould wall and the solidified shell, in case the melting of the powder produces an uneven phenomenon in a part when the powder becomes to be in a molten state on the molten steel surface and flows into the mould wall surface, a part in which the melting is slow exists in said melt, presents the form of solid or semi-melt, makes projections in irregular positions in the lubricating film produced on the mould wall surface and makes thick parts in the form of points in the lubricating film. Therefore, such part becomes less in the heat conduction from the molten steel to the mould wall than the normal lubricating film on the periphery, the cooling of the molten steel surface delays in this part, the solidified shell formation and growth at the same time delays, a solidification is formed early on the periphery with the lapse of time, therefore the periphery shrinks quickly, performs a pulling action on the part in which the solidification is late and produces cracks. Such flaws are difficult to remove by the sub sequent flaw removing operation as described above.

2 m n s r late senses! f resees t o a mould in w hic hmolt en ferritic stainless steel is cast by a cgn ti nugys cast i ngprocess which lubricates the mould wall with a melting velocity coinciding with the casting velocity and a uniform fluidity without unevenly melting the adding powder as described above and at the same time can prevent oxidization and keep warmth before melting on the upper surface of the molten steel and has it as an object to obtain ferritic stainless steel ingots having no surface flaw.

"[hgieature of the present invention is an agent for addingJcLa mould in which molten rmnc stiii? steeLjsgast by ,a continuous casting process characterizcdhmntainipg 20 to 35 percent by weight of fly ash, 30 to 40 percent by weight of Portland ggmggt @t dLQLbLsstfurnfi g sl g. 2.01. .21 per sntbxxslsmgfi QUQI PQL 2 .t e iaercem by. wish! o e s. 9! more .013 carbonate, silicate and the like, 5 to 10 percent by weight of one or more of a fluoride, silica-fluoride and th ik a ifilewmrcnnmmshuimsfiimrmf. such cart onaeeoas substannes as m ss. srsph t jaq gharcgal, showing a melting point of l,00O to 1 ,100C. and a viscosity of 0.1 to 5.0 poise at l,500C. and having an average particle size less than meshes.

By the way, in the specification. the percentage is shown by weight unless otherwise specified.

That is to say, the agent of the present invention has no bad influence on molten steels, does not impair the nozzle and keeps a viscosity adapted to a lubricating action from just before the beginning of the solidification of the molten steel to just after the solidification.

The mixed raw materials giving these properties have the above mentioned kinds and percentages of components, particle size, melting point and viscosity. They are homogeneously mixed together and are gradually added to the upper surface of a molten steel poured to a fixed height through a tundish nozzle immersed in the mould.

A manner of using the agent of the present invention shall be explained with reference to the accompanying drawing, which is a sectioned view of an embodyment of working the present invention.

In the drawing, when a molten steel 3 is poured into a mold 4 through a imersion nozzle 2 from a tundish 1 until the molten steel bath surface reaches a fixed height, the agent according to the present invention is added to the molten steel bath surface by either manpower or mechanical operation so as to uniformly cover the bath surface. The agent forms a melt layer 5 from below due to the heat of the molten steel 3, flows onto the mould wall so as to form a lubricating film 8, is deposited on the surface of the cast ingot and is led together with the cast ingot out of the mould. The unmolten powder layer 6 gradually melts to supplement the lubricating film. When the unmolten powder layer 6 is consumed, the agent is additionally put in. 7 shows a solidified layer ofthe molten steel.

As the agent of the present invention contains respective components in such percentages as is specified in the above mentioned subject matter of the present invention, the expected effect of the present invention is attained by the combined effects of the respective components. The reasons for limiting the component, percentage, granularity, melting point and viscosity of the composition shall be detailed in the following.

It is necessary that the melting point of the agent of the present invention should be l,000 to l',l00C. When it is less than l,000C, the velocity of the agent to melt in contact with the molten steel is so high that the amount of production of the melt required for the casting velocity of the molten steel is exceeded, the melt on the molten steel bath surface becomes excessive, carbon among the components is consumed so early that the agent must be more additionally put in to keep the reducing atmosphere and thus the agent is used in vain. In case the melting point exceeds l,l00C, the melting velocity is so low that no sufficient lubricating film can be provided. If the viscosity at l,500C is less than 0.1 poise, the fluidity of the melt is so high that it is impossible to form a favorable lubricating film. In case it exceeds 5.0 poise, the lubricating film does not well develop between the solidified shell of the molten steel and the surface of the mould. This also causes flaws on the surface of the cast ingot and is improper. Therefore, in order to make the melting velocity high and uniform, the particle size of the mixed raw material is made less than 100 meshes. When they exceed I00 meshes, the melting velocity becomes partly high or low. The fly ash among the mixed raw materials consists predominantly of aluminum silicate, has once passed through a molten state in the producing process and is high in the fusibility. Its mixing rate is proper at 20 to 35 percent. If it exceeds 35 percent, SiO, is so high that the viscosity of the melt is elevated and no proper lubricating film is produced. If it is less than 20 percent, SiO, is so low that the other components increase, the melting point rises, the fusibility is impaired and the nozzle is damaged. wof Eortlan dgement and b la st f u r r tace slag consists predominantly of basic t 8 l C l ur n aluminurp siljeait? has passed through a half-molten or molten state in the producing process and is therefore also high in the fusibility. Its mixing rate is proper at 30 to 40 percent. If it exceeds 40%, CaO becomes so high that the basicity rises, the melting point becomes high, the meltability is reduced and the nozzle is damaged. If it is less than 30 percent, SiO, becomes so high that the viscosity rises and the lubricating property deteriorates. Either is improper. In the case of making t h e n 1elt, a part of thefluorspgngegomes a caO source anilfififiaitof it remains CaF, as it is iii c1355 melting agent toredu ce the viscosity. Its mixing rate is the best at 20 to 27 percent. If it exceeds 27 percent, CaO increases, the basicity becomes high and the nozzle is damaged. [fit is less than 20 percent, the action as of a melting agent is so weak that the slag making object can not be attained. Anyof such carbonates and riljc ates gspqtassigm ga rbonate, sodium carbonate and sodium metasilicate and the like is used to reduce the melting point of the melt as a basic melting agent. Its mixing rate is the best at 2 to 15 percent. If it exceeds 15 percent, the melting point of the melt is reduced more than is that necessary, the agent is wasted and the etching of the immersion nozzle is accelerated. If it is less than 2 percent, the action as of the melting agent is impossible. Any of such fluorides and silicofluorides as sodium fluoride and sodiumsilicofluoride and the like is added to reduce the viscosity of the melt. It mixing rate is optimum at 5 to l0 percent. Ifit exceeds 10 percent, the powderness becomes so low that the production of the lubricating film becomes unfavorable. If it is less than 5 percent, there is no effect of reducing the viscosity. Qqke graphite or charcoal is added as a car; bon source so that the agentmay have a reducing ntmosphere and has effec ts of preventing t he increase ofl molt en s te el when the agent is added and of preventing the heat absorption from the molten steel by the agent itself by burning and generating heat. lts mixing rate is proper at 5 to ID percent. If it exceeds 10 percent, carbon is likely to be added to the molten steel or particularly of a low carbon stainless steel. If it is less than 5 percent, the reducing force is so weak that the increase of FeO can not be prevented.

The proper amount of use of the agent is 0.5 to 1.0 kg/ton of the molten steel in a slab and 1.0 to 2.0 kg/ton of the molten steel in a billet or bloom. If such amount of use as matches the amount led out as deposited on the cast ingot is added, the object is attained.

An example of the present invention is shown in the following.

The apparatus was a slab casting machine using a immersion nozzle. Six cast ingots of dimensions of I56 mm thick X 1,040 mm wide X 8,000 mm long were taken (the bad parts at the forward end and tail part were cut off) per charge. Each cast ingot was made one section of length 1 meter. The surface flaw index on the entire surface of the cast ingot jivas'd'eterrhinedby in- Sui-law: flaw index Nutnlmr of sections lmving'fluws:

Nulnbi-r of sections of east. ingots Examples of mixing the agent; were as in thevfollow ingtable.

Component kind of agent I amount of use of agent L0 (in kg/ ton) average surface flaw 0 0 O 0 7 8 index No. l No.2 No.3 No.4 No.5 No.6

ln Examples 1 to 4 of the above examples were used agents of the present invention. In Comparison l was used a high viscosity additive. ln Comparison 2 was .used a low-viscosity additive. In all the examples in ,which were used the a ents of the present invention,

W ites? Kind ofsteel: l8%Cr... "M

examexam- 'ple l ple 2 there was no surface aw at all. In the case of Comparison l, theviscosity was so high that no sufficient lubricating film could be formed, the residue had to be scraped off and the workability was low. In the case of Comparison 2, on the contrary, the viscosity was too low, the melting velocity was too high and the adding amount increased but the lubricating film had no proper property and surface flaws were produced.

- What We'Claim is:

I. An agent for improving the surfaces of products in the continuous casting in a mold of molten ferritic stainless steel by way of lubricating the mold well with a melting velocity coincident with the casting velocity and a uniform fluidity without any uneven melting of the agent comprising parts by weight of:

- 20 to percent of fly ash,

-30 to percent of Portland cement and blast furnace slag, g 20 to 27 percent of fluorspar,

2 to 15 percent of a carbonate or silicate from the group consisting of potassium carbonate and sodi- B um carbonate and sodium metasilicate,

.. 5 to 10 percent of a fluoride or silicofluoride from the group consisting of sodium fluoride and sodium silicofluoride,and

. f to lO percent by weight of a carbonaceous substance from the group consisting of coke and graphite and charcoal, i and having a melting point 6r l,000 to l,l00C and a viscosity of 0.1 to 5.0 poise at'l,500C and an average particle ,size less than mesh. 

